Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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Serum thyroglobulin 

Serum thyroglobulin (Tg) levels correlate roughly with the quantity of residual or recurrent functional follicular or papillary thyroid cancer (and any remaining benign thyroid tissue). Tg is roughly the "colloid" and the precursor to T3 & T4. But a positive/elevated or rising level excellently correlates with presence of residual/recurrent differentiated thyroid disease. One does not have to discontinue Synthroid-type thyroid supplementation prior to Tg testing. 

Differentiated thyroid cancer is treated with total or near-total thyroidectomy followed 4-6 weeks postop with remnant ablation I131 therapy. The basis of postablation follow-up is Tg measurement and cervical ultrasound. A study with post-ablation whole body I131 scan found lesions in 6.3-8.5% of patients with undetectible postablation Tg.

Tg is not too stable in frozen samples and best tested within 24 hours of drawing the sample2. Tg is low or undetectable in factitious hyperthyroidism and high in all other types of hyperthyroidism.

Serum Tg levels, otherwise, are proportional to:

  • amount of benign or malignant thyroid mass that produces Tg (one cannot track a thyroid cancer post-operatively if it is not a Tg producer).
  • the amount of stimulation of TSH receptor on the thyroid cells.
  • the amount of thyroid folliculocentric inflammation that results in increased release of Tg.

Anti-thyroglobulin (anti-Tg) is an endogenous auto antibody to thyroglobulin, and its presence is a confirmation test for a diagnosis of Hashimoto's thyroiditis; present in significant titers in Hashimoto's thyroiditis and Grave's disease (which are detectible in the oncologic thyroidectomy specimen). Presence of, or elevated levels of, this antibody (or of heterophile antibodies) or "hook effect" may cause problems in tests to determine a patient's serum thyroglobulin level3. Of 47 postablation patients with undetectible Tg but positive whole body scans: 23% had anti-Tg elevations or heterophile antibodies; no reason for discordance was found in 20% of cases3.

References:

  1. thyroid tests Practice Guidelines, National Academy of Clinical Biochemistry (NACB), USA.
  2. Gao Y, et. al., "Serum Thyroglobulin Stability for Immunoassay", Labmedicine 36(10):618-620, October 2007.
  3. Giovanella L., et. al., via Clinical Abstracts, CAP TODAY Jan. 2012, "Undetectable thyroglobulin in patients with differentiated thyroid carcinoma and residual radioiodine uptake on a postablation whole-body scan", Clin. Nucl. Med., 36(2):109-112, Feb. 2011.

(posted 25 June 2002 latest addition 4 February 2012)

 
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